Particle production from an expanding classical color electromagnetic field is extensively studied, motivated by the early stage dynamics of ultrarelativistic heavy ion collisions. We develop a formalism at one-loop order to compute the particle spectra by canonically quantizing quark, gluon, and ghost fluctuations under the presence of such an expanding classical color background field; the canonical quantization is done in the $\tau \text{−}\eta$ coordinates in order to take into account manifestly the expanding geometry. As a demonstration, we model the expanding classical color background field by a boost-invariantly expanding homogeneous color electric field with lifetime $T$, for which we obtain analytically the quark and gluon production spectra by solving the equations of motion of QCD nonperturbatively with respect to the color electric field. In this paper we study (i) the finite lifetime effect, which is found to modify significantly the particle spectra from those expected from the Schwinger formula; (ii) the difference between the quark and gluon production; and (iii) the quark mass dependence of the production spectra. Implications of these results to ultrarelativistic heavy ion collisions are also discussed.

We employ an Einstein-Maxwell-Dilaton (EMD) holographic model, which is known to be in good agreement with lattice results for the QCD equation of state with ($2+1$) flavors and physical quark masses, to investigate the temperature and baryon chemical potential dependence of the susceptibilities, conductivities, and diffusion coefficients associated with baryon, electric, and strangeness conserved charges. We also determine how the bulk and shear viscosities of the plasma vary in the plane of temperature and baryon chemical potential. The diffusion of conserved charges and the hydrodynamic viscosities in a baryon rich quark-gluon plasma are found to be suppressed with respect to the zero net baryon case. The transition temperatures associated with equilibrium and non-equilibrium quantities are determined as a function of the baryon chemical potential for the first time. Because of the crossover nature of the QCD phase transition even at moderately large values of the chemical potential, we find that the transition temperatures associated with different quantities are spread in the interval between 130–200 MeV and they all decrease with increasing baryon chemical potential.

Exploiting certain robust topological inputs from the skyrmion description of compressed baryonic matter with a scale-chiral symmetric Lagrangian, we predict the equation of state that is consistent with the properties of nuclear matter at the equilibrium density, supports the maximum mass of massive compact star $\sim 2M_{\odot }$ and surprisingly gives the sound velocity close to the “conformal velocity” $1/\sqrt{3}$ at densities $\gtrsim 3n_0$. At the core of this result is the observation that parity-doubling occurs in the nucleon structure as density goes above $\sim 2n_0$ with a chiral-singlet mass $m_0\sim (0.6–0.9)m_N$, hinting at a possible up-to-date unsuspected source of proton mass and an emergence at high density of scale symmetry and flavor local symmetry, both hidden in the QCD vacuum.

The volume inside a Ryu-Takayanagi surface has been conjectured to be related to the complexity of subregions of the boundary field theory. Here, we study the behavior of this volume analytically, when the entangling surface has a strip geometry. We perform systematic expansions in the low- and high-temperature regimes for AdS-Schwarzschild and RN-AdS black holes. In the latter regime, we point out spurious divergences that might occur due to the limitations of a near horizon expansion. A similar analysis is performed for extremal black holes and, at large charge, we find that there might be some new features of the volume as compared to the area. Finally, we numerically study a four-dimensional RN-AdS black hole in global AdS, the entangling surface being a sphere. We find that the holographic complexity captures essentially the same information as the entanglement entropy, as far as phase transitions are concerned.

We derive the generalization of the Knizhnik-Zamolodchikov equation (KZE) associated with the Ding-Iohara-Miki algebra $U_{q,t}({\widehat{\widehat{\mathfrak{gl}}}}_1)$. We demonstrate that certain refined topological string amplitudes satisfy these equations and find that the braiding transformations are performed by the $\mathcal{R}$ matrix of $U_{q,t}({\widehat{\widehat{\mathfrak{gl}}}}_1)$. The resulting system is the uplifting of the ${\widehat{\mathfrak{u}}}_1$ Wess-Zumino-Witten model. The solutions to the $(q,t)$ KZE are identified with the (spectral dual of) building blocks of the Nekrasov partition function for five-dimensional linear quiver gauge theories. We also construct an elliptic version of the KZE and discuss its modular and monodromy properties, the latter being related to a dual version of the KZE.

We study the Fock quantization of a free Dirac field in $2+1$-dimensional backgrounds which are conformally ultrastatic, with a time-dependent conformal factor. As it is typical for field theories, there is an infinite ambiguity in the Fock representation of the canonical anticommutation relations. Different choices may lead to unitarily inequivalent theories that describe different physics. To remove this ambiguity one usually requires that the vacuum be invariant under the unitary transformations that implement the symmetries of the equations of motion. However, in nonstationary backgrounds, where time translation is not a symmetry transformation, the requirement of vacuum invariance is in general not enough to fix completely the Fock representation. We show that this problem is overcome in the considered scenario by demanding, in addition, a unitarily implementable nontrivial quantum dynamics. The combined imposition of these conditions selects a unique family of equivalent Fock representations. Moreover, one also obtains an essentially unique splitting of the time variation of the Dirac field into an explicit dependence on the background scale factor and a quantum evolution of the corresponding creation and annihilation operators.

We study the canonical description of the axisymmetric vacuum in $2+1$-dimensional gravity, treating Einstein’s gravity as a Chern-Simons gauge theory on a manifold with the restriction that the dreibein is invertible. Our treatment is in the spirit of Kuchař’s description of the Schwarzschild black hole in $3+1$ dimensions, where the mass and angular momentum are expressed in terms of the canonical variables and a series of canonical transformations that turn the curvature coordinates and their conjugate momenta into new canonical variables is performed. In their final form, the constraints are seen to require that the momenta conjugate to the Killing time and curvature radius vanish, and what remains is the mass, the angular momentum, and their conjugate momenta, which we derive. The Wheeler-DeWitt equation is trivial and describes time independent systems with wave functions described only by the total mass and total angular momentum.

We derive a general set of acceptable junction conditions for $F(T)$ gravity via the variational principle. The analysis is valid for both the traditional form of $F(T)$ gravity theory as well as the more recently introduced Lorentz covariant theory of Krššák and Saridakis. We find that the general junction conditions derived, when applied to simple cases such as highly symmetric static or time dependent geometries (such as spherical symmetry), imply both the Synge junction conditions as well as the Israel-Sen-Lanczos-Darmois junction conditions of general relativity. In more complicated scenarios the junction conditions derived do not generally imply the well-known junction conditions of general relativity. However, the junction conditions of de la Cruz-Dombriz et al. make up an interesting subset of this more general case.

Recently, Hawking, Perry and Strominger described a physical process that implants supertranslational hair on a Schwarzschild black hole by an infalling matter shock wave without spherical symmetry. Using the Bondi-Metzner-Sachs-type symmetries of the Rindler horizon, we present an analogous process that implants supertranslational hair on a Rindler horizon by a matter shock wave without planar symmetry, and we investigate the corresponding memory effect on the Rindler family of uniformly linearly accelerated observers. We assume each observer to remain linearly uniformly accelerated through the wave, in the sense of the curved spacetime generalization of the Letaw-Frenet equations. Starting with a family of observers who follow the orbits of a single boost Killing vector before the wave, we find that after the wave has passed, each observer still follows the orbit of a boost Killing vector but this boost differs from trajectory to trajectory, and the trajectory dependence carries a memory of the planar inhomogeneity of the wave. We anticipate this classical memory phenomenon to have a counterpart in Rindler space quantum field theory.

Slow-roll inflation can become eternal if the quantum variance of the inflaton field around its slowly rolling classical trajectory is converted into a distribution of classical spacetimes inflating at different rates, and if the variance is large enough compared to the rate of classical rolling that the probability of an increased rate of expansion is sufficiently high. Both of these criteria depend sensitively on whether and how perturbation modes of the inflaton interact and decohere. Decoherence is inevitable as a result of gravitationally sourced interactions whose strength are proportional to the slow-roll parameters. However, the weakness of these interactions means that decoherence is typically delayed until several Hubble times after modes grow beyond the Hubble scale. We present perturbative evidence that decoherence of long-wavelength inflaton modes indeed leads to an ensemble of classical spacetimes with differing cosmological evolutions. We introduce the notion of per-branch observables—expectation values with respect to the different decohered branches of the wave function—and show that the evolution of modes on individual branches varies from branch to branch. Thus, single-field slow-roll inflation fulfills the quantum-mechanical criteria required for the validity of the standard picture of eternal inflation. For a given potential, the delayed decoherence can lead to slight quantitative adjustments to the regime in which the inflaton undergoes eternal inflation.

To explore the neutrino physics in the framework of Finsler geometry, we perform constraints on five cosmological models using the most stringent constraint we can provide so far. For the first time, we give the 95% limits of the total mass of three active neutrinos $\mathrm{\Sigma }{m}_{\nu }$ for three Finslerian models in the presence of massive neutrinos. We find that the base Finslerian model, a two-parameter extension to the $\mathrm{\Lambda }\mathrm{CDM}$ model based on the Finsler geometry, can fit better to current data than the other four models, and that the values of constrained effective typical parameters $\alpha$ and $\beta$ in four Finslerian models are all consistent with zero at the $1\sigma$ confidence level (CL), indicating that four Finslerian models just deviate very slightly from the $\mathrm{\Lambda }\mathrm{CDM}$ model. For the base Finslerian model with a constant equation of state (EoS) of dark energy (DE) and massive neutrinos, we obtain a tighter constraint on the EoS of DE, which is more stringent than Planck’s prediction by one order of magnitude. For the nonflat base Finslerian model with massive neutrinos, we find that our measured value of spatial curvature is in a strong tension with a flat universe at the $2.45\sigma$ CL. However, if fixing $\mathrm{\Sigma }{m}_{\nu }=0.06\mathrm{eV}$ with a normal hierarchy, this tension vanishes, i.e., a flat universe is still preferred in the nonflat base Finslerian model. We also find that the current $H_0$ tension can be effectively alleviated by four Finslerian models.

Production of axionlike particles (ALPs) by primordial magnetic fields may have significant impacts on cosmology. We discuss the production of ALPs in the presence of the primordial magnetic fields. We find a region of the ALP mass and photon coupling which realizes the observed properties of the dark matter with appropriate initial conditions for the magnetic fields. This region may be interesting in light of recent indications for the 3.5 keV lines from galaxy clusters. For a small axion mass, a region of previously allowed parameter spaces is excluded by overproduction of ALPs as a hot/warm dark matter component. Since the abundance of ALPs strongly depends on the initial conditions of primordial magnetic fields, our results provide implications for scenarios of magnetogenesis.

A detailed dynamical analysis for a bulk viscosity model in the full Israel-Stewart formalism for a spatially flat Friedmann-Robertson-Walker universe is performed. In our study we have considered the total cosmic fluid constituted by radiation, dark matter, and dark energy. The dark matter fluid is treated as an imperfect fluid which has a bulk viscosity that depends on its energy density in the usual form $\xi ({\rho }_m)={\xi }_0{\rho }_m^{1/2}$, whereas the other components are assumed to behave as perfect fluids with constant equation of state parameter. We show that the thermal history of the Universe is reproduced provided that the viscous coefficient satisfies the condition ${\xi }_0\ll 1$, either for a zero or a suitable nonzero coupling between dark energy and viscous dark matter. In this case, the final attractor is a dark-energy-dominated, accelerating universe, with an effective equation of state parameter in the quintessence-like, cosmological constant-like, or phantom-like regime, in agreement with observations. As our main result, we show that in order to obtain a viable cosmological evolution and at the same time alleviating the cosmological coincidence problem via the mechanism of scaling solution, an explicit interaction between dark energy and viscous dark matter seems inevitable. This result is consistent with the well-known fact that models where dark matter and dark energy interact with each other have been proposed to solve the coincidence problem. Furthermore, by insisting on above, we show that in the present context a phantom nature of this interacting dark energy fluid is also favored.

The energy threshold of a cryogenic calorimeter can be lowered by reducing its size. This is of importance since the resulting increase in signal rate enables new approaches in rare-event searches, including the detection of MeV mass dark matter and coherent scattering of reactor or solar neutrinos. A scaling law for energy threshold vs detector size is given. We analyze the possibility of lowering the threshold of a gram-scale cryogenic calorimeter to the few eV regime. A prototype 0.5 g ${\mathrm{Al}}_2{\mathrm{O}}_3$ device achieved an energy threshold of $E_{\text{th}}=(19.7\pm 0.9)\mathrm{eV}$, the lowest value reported for a macroscopic calorimeter.

Possible manifestations of the isospin-breaking mixing of the $a_0^0(980)$ and $f_0(980)$ resonances are analyzed in the $D^0\to K_S^0{\pi }^{+}{\pi }^{-}$ and $D^0\to K_S^0\eta {\pi }^0$ decays. It is shown that the $a_0^0(980)-f_0(980)$ mixing has the most influence on the ${\pi }^{+}{\pi }^{-}$ mass spectrum in the decay $D^0\to K_S^0{\pi }^{+}{\pi }^{-}$. Owing to the $a_0^0(980)-f_0(980)$ mixing, the $f_0(980)$ peak in $D^0\to K_S^0{f}_0(980)\to K_S^0{\pi }^{+}{\pi }^{-}$ can experience distortions comparable with its size. The effect essentially depends on the relative phase between the amplitudes of the $D^0\to K_S^0{f}_0(980)$ and $D^0\to K_S^0{a}_0^0(980)$ transitions.

We suggest a novel experimental concept for detecting MeV-to-GeV-mass dark matter, in which the dark matter scatters off electrons in a scintillating target and produces a signal of one or a few photons. New large-area photodetectors are needed to measure the photon signal with negligible dark counts, which could be constructed from transition edge sensor (TES) or microwave kinetic inductance detector (MKID) technology. Alternatively, detecting two photons in coincidence may allow the use of conventional photodetectors like photomultiplier tubes. We describe why scintillators may have distinct advantages over other experiments searching for a low ionization signal from sub-GeV dark matter, as there are fewer potential sources of spurious backgrounds. We discuss various target choices, but focus on calculating the expected dark matter-electron scattering rates in three scintillating crystals: sodium iodide (NaI), cesium iodide (CsI), and gallium arsenide (GaAs). Among these, GaAs has the lowest band gap (1.52 eV) compared to NaI (5.9 eV) or CsI (6.4 eV), which in principle allows it to probe dark matter masses as low as $\sim 0.5\mathrm{MeV}$, compared to $\sim 1.5\mathrm{MeV}$ with NaI or CsI. We compare these scattering rates with those expected in silicon (Si) and germanium (Ge). The proposed experimental concept presents an important complementary path to existing efforts, and its potential advantages may make it the most sensitive direct-detection probe of dark matter down to MeV masses.

In this work, the lepton-number-violating processes in $|\mathrm{\Delta }L|=2$ decays of ${\mathrm{\Lambda }}_b^0$ baryon, ${\mathrm{\Lambda }}_b^0\to p{\pi }^{+}{\mu }^{-}{\mu }^{-}$ and ${\mathrm{\Lambda }}_b^0\to {\mathrm{\Lambda }}_c^{+}{\pi }^{+}{\mu }^{-}{\mu }^{-}$, are investigated for the first time, via an intermediate on-shell Majorana neutrino $N$ with a mass in the GeV scale. We explore the experimental sensitivity of these dimuon channels at the LHCb and CMS experiments, in which heavy neutrino lifetimes in the accessible ranges of ${\tau }_N=[1,100,1000]\mathrm{ps}$ are considered. For a integrated luminosity collected of 10 and $50{\mathrm{fb}}^{-1}$ at the LHCb and 30, 300, and $3000{\mathrm{fb}}^{-1}$ at the CMS, we found significant sensitivity on branching fractions of the order $\mathrm{BR}({\mathrm{\Lambda }}_b^0\to p{\pi }^{+}{\mu }^{-}{\mu }^{-})\lesssim \mathcal{O}({10}^{-9}–{10}^{-8})$ and $\mathrm{BR}({\mathrm{\Lambda }}_b^0\to {\mathrm{\Lambda }}_c^{+}{\pi }^{+}{\mu }^{-}{\mu }^{-})\lesssim \mathcal{O}({10}^{-8}–{10}^{-7})$. Exclusion regions on the parameter space ($m_N$, $|V_{\mu N}{|}^2$) associated with the heavy neutrino are presented and compared with those from $K^{-}\to {\pi }^{+}{\mu }^{-}{\mu }^{-}$ (NA48/2) and $B^{-}\to {\pi }^{+}{\mu }^{-}{\mu }^{-}$ (LHCb) as well as by different search strategies such as NA3, CHARMII, NuTeV, Belle, and DELPHI.

We analyze the recent hints of lepton flavor universality violations in semileptonic $B$ decays within a general effective field theory (EFT) based on a $U(2{)}^n$ flavor symmetry acting on the light generations of Standard Model (SM) fermions. We analyze in particular the consistency of these anomalies with the tight constraints on various low-energy observables in $B$ and $\tau$ physics. We show that, with a moderate fine-tuning, a consistent picture for all low-energy observables can be obtained under the additional dynamical assumption that the new physics (NP) sector is coupled preferentially to third-generation SM fermions. We discuss how this dynamical assumption can be implemented in general terms within the EFT, and we identify a series of observables in $\tau$ decays which could provide further evidence of this NP framework.

The $P_5^{\prime }$ and $R_K$ anomalies, recently observed by the LHCb Collaboration in $B\to K^{(*)}$ transitions, may indicate the existence of a new $Z^{\prime }$ boson, which may arise from gauged $L_{\mu }-L_{\tau }$ symmetry. Flavor-changing neutral current $Z^{\prime }$ couplings, such as $tc{Z}^{\prime }$, can be induced by the presence of extra vector-like quarks. In this paper we study the LHC signatures of the induced right-handed $tc{Z}^{\prime }$ coupling that is inspired by, but not directly linked to, the $B\to K^{(*)}$ anomalies. The specific processes studied are $cg\to t{Z}^{\prime }$ and its conjugate process, each followed by $Z^{\prime }\to {\mu }^{+}{\mu }^{-}$. By constructing an effective theory for the $tc{Z}^{\prime }$ coupling, we first explore in a model-independent way the discovery potential of such a $Z^{\prime }$ at the 14 TeV LHC with 300 and $3000{\mathrm{fb}}^{-1}$ integrated luminosities. We then reinterpret the model-independent results within the gauged $L_{\mu }-L_{\tau }$ model. In connection with $tc{Z}^{\prime }$, the model also implies the existence of a flavor-conserving $cc{Z}^{\prime }$ coupling, which can drive the $c\overline{c}\to Z^{\prime }\to {\mu }^{+}{\mu }^{-}$ process. Our study shows that existing LHC results for dimuon resonance searches already constrain the $cc{Z}^{\prime }$ coupling, and that the $Z^{\prime }$ can be discovered in either or both of the $cg\to t{Z}^{\prime }$ and $c\overline{c}\to Z^{\prime }$ processes. We further discuss the sensitivity to the left-handed $tc{Z}^{\prime }$ coupling and find that the coupling values favored by the $B\to K^{(*)}$ anomalies lie slightly below the LHC discovery reach even with $3000{\mathrm{fb}}^{-1}$.